Common Types and Design Rules of Mold Gates

The manually removed gate requires the operator to process and cut the gate again. The reasons for its use include:

1. The gate is too large and must be moved outside the mold before cutting.

2. For plastics (such as PVC) that are sensitive to shear stress, automatic removal gates should be avoided.

3. When the melt glue from different directions flows through a large cross-sectional area at the same time and the fiber orientation is required, the automatic removal gate should be avoided.

– Direct gate, also known as sprue gate, is usually used in single-cavity molds. Plastic directly fills the mold cavity from the sprue with minimum pressure drop. The solidification of the direct gate is controlled by the thickness of the plastic part, not the gate thickness. Generally, the shrinkage of plastic parts near the direct gate is small, but there is a large amount of shrinkage at the direct gate, resulting in a large amount of tensile stress at the gate. The diameter of the entrance end of the direct gate is related to the diameter of the ejector nozzle. The diameter of the gate entrance must be more than 1mm larger than the diameter of the ejector nozzle. The standard vertical runner bushing has a 2.4 ° taper opening to the plastic part end, so the length of the direct gate controls the gate root diameter of the plastic part end. The gate root diameter should be at least 1.5 mm larger than the thickness of the plastic part, or about twice the thickness of the plastic part. The cone angle of the direct gate shall be at least 1 °. Too small cone angle may make the vertical gate unable to separate from the vertical gate bushing when ejecting; Too large cone angle wastes plastic and prolongs cooling time. The processing cost of the vertical runner with a non-standard cone angle is high, but it has no benefit.

– The tab gate is usually used for flat plastic parts or thin plastic parts to reduce the shear stress in the mold cavity. The high shear stress around the gate only occurs in the auxiliary convex and will be cut off after forming. The convex gate is often used in the forming of PC, acrylic, SAN, ABS, and other resins. The minimum width of the convex plate is 6.4mm, and the minimum thickness is 75% of the cavity thickness.

– Edge gate, also known as standard gate, is usually located on the parting line of the mold and filled from the side, above or below the plastic part. The typical edge gate size is 6%~75% of the plastic part thickness, or 0.4~6.4 mm, and the width is 1.6~12.7 mm. The gate surface length should not exceed 1.0 mm, and the optimal value is 0.5 mm.

– Overlap gate is similar to an edge gate, but the overlapping gate overlaps with the side wall or surface of the plastic part. Overlapping gates are often used to prevent jet effects. The typical overlapping gate size is 0.4~6.4 mm thick and 1.6~12.7 mm wide.

– Fan gate is a wide-sided gate with gradually changing thickness. It has a large filling area and can quickly fill large plastic parts with molten glue. Large plastic parts are very concerned about warpage and dimensional stability. The use of fan-shaped gates can make the melt front of large plastic parts evenly fill the mold cavity.

– Disk gate, also known as diaphragm gate, is usually used for plastic parts with openings on the inner side, which require high coaxially, or plastic parts that do not allow sutures. Basically, the disc gate is a burr-like gate used at the inner edge of the plastic part. The molten glue is filled into the mold cavity from the coaxial vertical gate, and it is easy to obtain the plastic part with a uniform flow of molten glue. The thickness of the disk gate is usually 0.25~1.27 mm.

– Ring gate is also applied to cylindrical or circular plastic parts. The plastic first surrounds the mold center, and then fills down along the circular pipe. The annular gate is not applicable to all plastic parts. The thickness of the annular gate is usually 0.25~1.6 mm.

– Spoke gate, also known as a four-point gate or cross gate, is suitable for tubular plastic parts, with the advantages of easy removal of the gate and saving plastic. However, it may cause stitches, and it is impossible to obtain perfect roundness. The radial gate is usually 0.8~4.8 mm thick and 1.6~6.4 mm wide.

– Film gate is also called the flash gate. A film gate is similar to a ring gate, but it is used for plastic parts with flat edges. It has a flat gate, and the gate width can span the whole or part of the hole edge. The film gate is applicable to acrylic plastic parts and is often used in large and flat plastic parts to maintain the minimum amount of warpage. The size of the membrane gate is very small, the thickness is about 0.25~0.63 mm, and the width is about 0.63 mm.